Method and system for remediation of groundwater contamination

ABSTRACT

A method for remediating a hydrocarbon-contaminated region of a subterranean body of groundwater to destroy or reduce the initial concentration levels of hydrocarbon contaminants. A plurality of mutually spaced wells are provided which intersect the groundwater region. A treating flow of acetic acid is provided from one or more of the wells into the groundwater region, to establish acidic conditions. A turbulent flow of an aqueous solution of ferrous ion into the groundwater region is generated for mixing with the acidified groundwater, thereby providing a catalyst for disassociation of hydrogen peroxide. A treating flow of hydrogen peroxide solution from one or more of the wells into the groundwater region is then provided, so that the hydrogen peroxide may undergo a Fenton-like reaction in the presence of the acidic conditions and ferrous ion to generate hydroxyl free radicals for oxidizing the contaminants. An apparatus system for practicing the method is also disclosed.

RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 08/017,478, now U.S. Pat. No. 5,286,141.

BACKGROUND ON INVENTION

This invention relates generally to the beneficial treatment oforganics-contaminated water, and more specifically relates to method andapparatus for remediating groundwater which has become contaminated withhydrocarbons, PCB's, aromatic solvents, chlorinated solvents, pesticidesand the like.

Groundwater contamination, typically arising from petroleum storage tankspills or from intentional or accidental discharge of liquidhydrocarbons or compositions containing same, has become a problem ofincreasing concern in virtually all areas of the world where humanactivities occur. Aside from contamination of this type which resultsfrom industrial complexes, it has unfortunately been found that evensuburban neighborhoods which would appear to be havens from suchphenomena, have increasingly been found to the consternation of theresidents to harbor pools of hydrocarbon pollutants, the source of whichis very commonly automobile service station sites at which antiquated orabandoned storage tanks have released gasoline, fuel oils, lubricantsand the like into the local groundwater. Other common sources of suchnoxious material can include dry cleaning establishments and/ormanufacturers or distributors of the tetrachloroethane which is used indry cleaning. Other well-known hazardous hydrocarbon materials includepolychlorinated phenols (e.g. PCB's), pentachlorophenols (PCP's), andvarious aliphatic and aromatic hydrocarbons, as for example gasoline,benzene, naphthalene and various petroleum and petroleum derivativeproducts. Certain particularly pernicious compounds of this type areoften considered under the grouping "BTEX", which is understood by thosefamiliar with the art to refer to benzene, toluene, ethyl benzene andthe xylenes (m-, p-, and o-). The BTEX content of groundwater or othercontaminated sites is frequently regarded as a principle measure of theacceptability of the water in question for human consumption and use andother purposes.

Various remediation techniques have been utilized in the past fortreatment of groundwater which has been thus contaminated. Among themost predominate type of systems in present use are those based onso-called "pump and treat" technology. In this method the contaminatedgroundwater and possibly a phase-separated product is withdrawn from arecovery well sunk into the groundwater and pumped to an above groundtreatment facility. Various treatment techniques are thereupon used,such as diffused air treatment and air stripping. Inline filters canalso be used; and similarly carbon adsorption can serve to removecontaminants from the displaced groundwater. Systems of the pump andtreat type are considered expensive to install and operate. In manyinstances they basically result in separation or adsorption of thecontaminants, and while purified water may result from the treatment,the problem often remains of disposing of the contaminants which havethus been separated.

In recent years increasing interest has also been evidenced inbioremediation technology. The technology has been of great interest,but its effective use in treating groundwater has been limited. Theprocedures are very complex, involving the use of expensive and complexreactors, and can cause adverse geochemical reactions, and can evenintroduce new toxic compounds beyond those which are being treated.

Pursuant to the foregoing, techniques have been sought which would serveto directly treat the contaminated groundwater in both effective andeconomical fashion.

It has long been recognized that the hydrocarbons representing thesource of contamination in the subject matter of interest, can byordinary chemical reactions be oxidized to harmless constituents. Inprinciple, all such hydrocarbons can under proper conditions be oxidizedto harmless end products, such as water and carbon dioxide. To date,practical methodology to achieve such results, however, have not beenwidely adopted. Among the strong oxidizing agents which in principlecould serve these purposes is hydrogen peroxide, a composition which isreadily available and at reasonable cost. Some efforts have indeed beenmade to utilize this oxidizing agent for these purposes. In Brown etal., U.S. Pat. No. 4,591,443, for example, an aqueous solutioncontaining hydrogen peroxide, together with a compound for controllingthe mobility of the aqueous solution by modifying the viscosity or otherflow properties, is introduced into a permeable subterranean formation.It is not contemplated that the groundwater can be treated directly inthis disclosure.

Forte et al., U.S. Pat. No. 4,167,973, discloses the use of strongoxidizing agents, which can include hydrogen peroxide, for treatingcontaminated water and the like which has been withdrawn from anunderground source and is thereupon treated in a mixing device. Themethodology is therefore of the pump and treat system type, and thetreatment of the groundwater is not in situ.

Other patents of interest include U.S. Pat. Nos. 4,927,293 to Campbell,and 4,978,508 to Hansen et al.

Among the other deficiencies of the prior art, is the failure to definea system wherein a strong oxidizing agent such as hydrogen peroxide maybe directly injected into groundwater in a manner such that it can reactin situ with the hydrocarbon contaminants present in same, while at thesame time providing techniques to assure the efficacy of the saidmethod.

Pursuant to the foregoing it may be regarded as an object of the presentinvention to provide a method and system which enable economical,effective and rapid treatment of groundwater contaminated withhydrocarbons, so as to destroy the said hydrocarbons or reduce same to alevel below that which is considered detrimental to human use.

It is a further object of the present invention to provide a method andapparatus of the foregoing character, which utilizes safe and readilyavailable treatment chemicals, and which moreover results in outputproducts which are harmless and safe.

It is a still further object of the invention to provide a method andapparatus which can be practiced with use of relatively simpleequipment, and by relatively unskilled personnel.

SUMMARY OF INVENTION

The present invention utilizes the well-known Fenton's reaction in whichhydrogen peroxide reacts with Fe⁺² ion to produce OH. free radicalaccording to the equation H₂ O₂ +Fe⁺² →OH.+OH⁻ +Fe⁺³. The OH. freeradical is an extremely powerful oxidizer which effectively reacts withorganic contaminants to produce carbon dioxide and water.

Thus in accordance with the present invention, a method is provided forremediating a hydrocarbon-contaminated region of a subterranean body ofgroundwater to destroy or reduce the initial concentration levels ofhydrocarbon contaminants. Pursuant to the invention a plurality ofmutually spaced wells are provided which intersect the groundwaterregion. A treating flow of acetic acid is provided from one or more ofthe wells into the groundwater region, to establish acidic conditionstherein. A turbulent flow of an aqueous solution of ferrous ion isintroduced into the groundwater region, for mixing with the acidifiedgroundwater, thereby providing a catalyst for disassociation of hydrogenperoxide. A treating flow of hydrogen peroxide solution is then providedfrom one or more of the wells into the groundwater region, the hydrogenperoxide undergoing a Fenton-like reaction in the presence of the acidicconditions and ferrous ion to generate hydroxyl free radicals foroxidizing the contaminants.

During the acidification step the groundwater region is typicallybrought to a pH of from 3.0 to 4.0. The existence of acceptablecontinuity and well interflow paths for the region are determined bymonitoring pH changes at each other of said wells as a function of timeto detect a pH drop of at least 0.2.

Between the acidification step and the introduction of ferrous ion, aswell as between the ferrous ion introduction and the addition ofhydrogen peroxide, potable water is injected from the same said wells inplace of acetic acid and ferrous ion solutions, to provide a transientbuffer zone between the compositions introduced during such stepsthereby delaying the reaction achieved in the final step until the plumehas extended further into the groundwater region.

Where acetic acid is used for the acidification step, it is typicallyflowed as a solution at a rate of 5 to 10 gallons/min, wherein saidsolution includes from 10% to 100% by weight of acetic acid. The totalamount of acetic acid flowed into the region is typically from 1 to 3%by volume of the effective volume of contaminated water which istreated, based on a 100% acetic acid solution. The Fe²⁺ ion is providedas an aqueous solution of ferrous sulfate heptahydrate, the total volumeof the solution flowed into said region being from 0.5 to 3% of theeffective volume of the contaminated water which is treated, based on a100% by weight solution of said heptahydrate. The treating flow ofhydrogen peroxide is at the typical rate of 0.1 to 10 gallons ofhydrogen peroxide per minute per well, expressed on the basis of a 35%by weight solution of hydrogen peroxide.

The total said treating flow of hydrogen peroxide solution is typically1 to 5% by weight of the effective volume of contaminated water which istreated, expressed on the basis of a 100% solution of hydrogen peroxide.

Pursuant to a further aspect of the invention there is provided a methodof remediating a hydrocarbon-contaminated subterranean static plume ofgroundwater to destroy or reduce the initial concentration levels ofhydrocarbon contaminants, comprising the steps of: providing a pluralityof mutually spaced wells intersecting said static plume groundwater;measuring the change in water depth at each of said wells followingatmospheric precipitation, to determine by common depth changes thelikelihood of said plume; confirming the existence of the static plumeby generating a test flow of a solution of hydrogen peroxide or aceticacid from one of said wells and monitoring the absence of pH changes ateach other of said wells as a function of time; and providing a treatingflow of solutions of acetic acid, of ferrous ion, and of hydrogenperoxide from each of said wells to establish a radial sweep about eachsaid well, the total volumes and respective concentrations of treatingsolutions being effective to bring about a Fenton-like reactiongenerating hydroxyl free radicals for oxidizing said contaminants.

Thus it will be seen that in the general mode of practicing theinvention, a method is provided for remediating ahydrocarbon-contaminated region of a subterranean body of groundwater todestroy or reduce the initial concentration levels of hydrocarboncontaminants, wherein acidic conditions are established at thegroundwater region; and flows of aqueous solutions of ferrous ion and ofhydrogen peroxide are introduced into the groundwater region, for mixingwith the acidified groundwater. The hydrogen peroxide thus undergoes aFenton-like reaction in the presence of the acidic conditions andferrous ion to generate hydroxyl free radicals for oxidizing saidcontaminants.

In a further aspect of the invention, a system is provided forremediating a hydrocarbon-contaminated region of a subterranean body ofgroundwater to destroy or reduce the initial concentration levels ofhydrocarbon contaminants. The system includes a plurality of mutuallyspaced wells which intersect the groundwater region. Means are providedfor pumping a treating flow of acetic acid from one or more of the wellsinto the groundwater region, to establish acidic conditions. Furthermeans serve to introduce a turbulent flow of an aqueous solution offerrous ion into the groundwater region, for mixing with the acidifiedgroundwater, thereby providing a catalyst for disassociation of hydrogenperoxide; and means are provided for pumping a treating flow of hydrogenperoxide solution from one or more of the wells into the groundwaterregion, the hydrogen peroxide undergoing a Fenton-like reaction in thepresence of the acidic conditions and ferrous ion to generate hydroxylfree radicals for oxidizing the contaminants.

In the course of practicing the invention, the treating flow isperiodically stopped and a determination made of the hydrocarboncontaminant levels at each said well, the process being continued untilthe initial contaminant concentration levels drop below predeterminedacceptable values. The treating flow may additionally contain reactionsurface enhancing reagents, i.e. reagents such as dispersions of lime orthe like, which increase or provide surfaces at which the reactionbetween the near-Fenton solution and the hydrocarbon contaminants mayoccur. Other additives can also be employed to modify the rheology ofthe treating flow; and stabilizers and the like may be present in thehydrogen peroxide solution to inhibit premature reaction ordecomposition of the oxidizer.

The reaction products of the method constitute innocuous substances,principally water and carbon dioxide predominantly with some associatedoxygen and trace element oxidations all of which are lower order ofconcentrations. Peroxide cleaves aromatic ring structures, and oxidizesthe resulting straight-chain or branched-chain alkanes. The oxidationproceeds through progressively shorter hydrocarbon chains, eventuallyresulting in carbon dioxide and water. The peroxide reduction leaves nohazardous residue itself. The hydrogen peroxide may be used inconcentrations of from about to 1% to 70% by weight solutions, which areavailable commercially from many sources.

Typical flow rates used in the foregoing process can be of the order of0.1 to 36 gallons of hydrogen peroxide solution per minute per well,expressed on the basis of a 35% by weight solution of hydrogen peroxide.

In a preferred mode of practicing the present invention, the existenceof acceptable continuity and well interflow paths for the groundwaterregion to be treated is established by initially generating a test flowof a solution of hydrogen peroxide from one of the wells and monitoringpH changes at each other of the wells as a function of time. A pH dropof at least 0.2 is considered to be indicative of satisfactoryconditions. The pH changes are characteristic of the REDOX reactionsinvolved in the invention and are believed to result from the formationof carboxylic acids during the reaction between the hydrogen peroxideand hydrocarbons. Typical such products are acetic acid and certainalkyls. None of these components are hazardous, but if desired, they canbe neutralized as part of the overall treatment process. Subsequent todetecting the said pH drop, a treating flow of the hydrogen peroxidesolution is then provided from one or more of the wells. The treatingflow is again periodically stopped and the hydrocarbon contaminantlevels measured at each well until the initial concentration levels dropbelow predetermined acceptable values. Initial acetic acid injectionalone can also be used to induce the above pH drop.

Typical treating flows are at the rate of 0.1 to 36 gallons of the threetreatment solutions per minute per well, depending in part upon theconcentrations of the solutions used and the contamination levels. Thetreating flow is provided under a pressure not more than the hydrostatichead relative to ground surface at the point of treating flow dischargefrom the well. If the pressure exceeds this, it is possible for some ofthe reactants to pass upwardly through the porous overburden and createundesirable conditions on the ground surface. Very typically in mostinstallations the treating flow is under a pressure of about 6 to 40psig, subject to the boundary condition indicated in the foregoing.

The total treating flow of the three treatment solutions will generallybe in the range of 0.1 to 10% by weight of the effective volume ofcontaminated water which is to be treated, expressed on the basis of a35% solution of hydrogen peroxide. The "effective volume" is consideredfor purposes of this specification includes not only the pooled orpossibly slowly flowing groundwater region per se, but as well theoverburden which defines the region between the top of the groundwaterand the overlying surface accessible to atmosphere. This is consideredappropriate in that the communication between overburden and groundwateris such that water can flow with relative ease between the surfaceoverburden and groundwater, and hence in calculating quantities oftreating reactants, account should desirably be taken of this factor."Effective volume" also reflects the apparent interflow from adjacentregions into the region being treated. Boundary interflow can beevaluated by observing how rapidly the pH may change as a function oftime at the various wells after a test flow is completed, i.e. arelatively rapid change will indicate that flow from adjacent regions isrelatively high, leading to an adjustment in the initially calculatedeffective volume of the order of 10 to 20%.

The total volume utilized in the test flow is typically 0.05 to 0.1% byweight of the effective volume of the contaminated water, expressed onthe basis of a 35% hydrogen peroxide solution unless free product (e.g.floating oils etc.) is present which requires volume increases offactors which can typically be as high as 10.

In typical treatment arrangements pursuant to the invention at leastthree injection wells are utilized which are spaced about the peripheryof the groundwater region to be treated. The test flow is injected atone said well and the pH changes are monitored at the other said wells.

In a further aspect of the invention, it has been found that in additionto the pH change serving as a sensitive indicator of interflow andcontinuity, temperature changes also resulting from the aforementionedREDOX reactions may serve as an additional monitoring parameter. Thus inthis aspect of the invention the temperature changes are monitored atone or more other of the wells during the test flow process. Atemperature rise of at least 2° F. at each well spaced from theinjection well is considered a confirmatory indicator of the acceptablecontinuity and well interflow paths.

In the special case in which a static plume is found to exist, samebeing indicated by observing following moderate atmosphericprecipitation that the water levels in the plurality of spaced wellsshow common changes in height, the treatment regime involves confirmingthe existence of the static plume by generating a test flow of the threetreating solutions from one of the said wells and monitoring the absenceof pH changes at each other of the said wells as a function of time. Atreating flow of the Fenton-like reactant solutions from each of thewells is then provided at a representative rate of 0.1 to 36gallons/minute to establish a radial sweep about each said well, thetotal volume of treating solution being again from 0.1 to 10% by weightof the effective volume of contaminated water expressed on the basis ofa 35% hydrogen peroxide solution.

BRIEF DESCRIPTION OF DRAWINGS

The invention is diagrammatically illustrated, by way of example, in thedrawings appended hereto in which:

FIG. 1 is plan elevational view, diagrammatic in nature of thetopography of a site at which groundwater is to be treated;

FIG. 2 is a cross-sectional view taken along the line 2--2' of FIG. 1,and illustrating in the subterranean characteristics of the mappedportion of FIG. 1; and

FIG. 3 is a schematic cross-sectional view through a representativemonitoring end injection well of the type utilized in FIGS. 1 and 2. Thecontrol elements used in connection with the method and system areschematically illustrated in this Figure.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring to FIGS. 1 and 2, plan and cross-sectional views are shown ofa typical site in which the method of the invention may be utilized.Contours and topography are indicated by appropriate indicia in feet andinches. The groundwater reservoir to be treated is shown in outline at10 in FIG. 1, at which it is seen that four monitoring and injectingwells 12, 14, 16 and 18 are provided, generally around the periphery ofthe groundwater reservoir 10 to be treated. As best seen in thecross-sectional view of FIG. 2, each of the wells extend to intersectgroundwater reservoir 10. Reservoir 10 may be considered to be pollutedwith various organic contaminants of the type previously discussed. Thegroundwater reservoir 10 lies atop an impermeable clay layer 20underneath which bedrock 22 is present. Atop the groundwater reservoir,in order is a silty sand with clay and some gravel layer 24; a siltysand with clay and gravel layer 26; and finally a sand with silt andgravel layer 28. The soil layers atop the reservoir are generally porousand permit with relative ease communication of atmospheric precipitationwith the said reservoir. The present reservoir 10 may be considered asnot being a static plume; i.e. flow to and from same is readilypossible, although obviously is impeded by the surrounding surfaces andboundaries.

Details of a specific monitoring and injection well 30 are seen in FIG.3. A borehole 32 is provided in which a well casing 34 typically of aPVC material, is inserted as a liner. This liner, as is well known inthe art, is provided beneath seal 35 with a slotted well screen 36, i.e.the PVC is provided with multiple fine slots to create the screenedeffect. A sand/gravel pack 37 surrounds slotted screen 36. An injectionstring 38 extends to the interior of the well. A valve 40 is providedand a temperature transducer 42 and a pressure transducer 44 areconnected to the upper, i.e. above-ground portion of injection string 38between valve 40 and a valve 46. A quick connect assembly is provided at48. Schematically shown in FIG. 2 are a series of supply tanks 50, 52,54, 56, 58 and 60, respectively being used for the hydrogen peroxidetreating solution, catalyst, stabilizer, enhancer, acids, and alkaliesas required. Additional tanks may be provided e.g. when more than onecatalyst is used. Pumps 62, 64, 66 and 68 may dispense these componentsto the quick connect assembly and thereby to the injection andmonitoring well 30. Each of the pumps are under control of a controlstation 70 including a control console 72. Monitoring display 74provides data and information to the operator, including pressures andtemperatures from the transducers at 42 and 44. A chart recorder 76 issimilarly provided at the control station 70. A portable test set 78 maybe used to establish such parameters as pH, temperature, salinity,conductivity and the like. When needed, deionized water from tank 80 andpotable water from tank 82 can also be provided via pumps 84 and 86 tothe quick connect assembly 48. The entire system is highly portable; anA.C. power generator 88 is provided, and may be driven by a gasoline orother motor. This provides power for all control units including thecentral control station 70. It will be appreciated that a monitoringflow can be withdrawn from the well, as can a treating or test flow beinjected via the well into the groundwater which the well intersects.

The volume of groundwater reservoir 10 is known in advance from theplurality of wells, which have served to establish the level of thereservoir and depth of the water in same, and the general contours ofsame. It will be clear that from these considerations the effectivevolume, i.e. including the reservoir and overburden is calculable--whicheffective volume may include a 10 to 20% additive factor for porous flowto adjacent zones which are lateral to the region of interest. In thecourse of operating the present system, and pursuant to the foregoingdiscussion, the existence of acceptable continuity and well interflowpaths for the region to be treated is established by generating a testflow from one of the wells and monitoring pH changes at the other of thewells as a function of time. A pH drop of at least 0.2 is taken asindication of satisfactory well interflow paths and continuity.Thereafter the treating flow of hydrogen peroxide solution is initiatedfrom the tank 62. As also mentioned, and in advance of this, aninitiation catalyst can be injected from tank 52, as can the otheradditives if desired, such as stabilizers from tank 54, enhancers fromtank 56, and acid and alkali adjustments from tanks 58 and 60.

Among the additives which may be utilized in the present process, aresilicate-based inorganic polymers which can serve as finely divided highsurface area powders used as adsorbent catalysts. Finely divided ironfilings and potable water can be used as an initiation catalyst byinjection in advance of the treating solutions. Other initiationcatalyst water solutions include molybdenum, nickel, silver, platinum,and gold, all of which can be added in catalytically effectivequantities. Powdered lime can be used as an enhancer with water toencourage saturated alkanes, i.e. unleaded gas and oil, to adsorb ontothe lime surface along with hydrogen peroxide. Other additives such ashydralizable polymers can be used to increase viscosity and controldiffusion through the groundwater. Various viscosity modifiers in apotable water mix can include ordinary compatible household laundrysoaps, mixtures of sodium hydroxide and sodium lauryl sulfate, lime,magnesium oxide, diatamaceous earth anionic, cationic and nonionicpolymers. Alkaline agent enhancers may be used to accelerate aromaticring structures dehalogenation and decomposition. Also, as known in theart of conducting reactions with hydrogen peroxide, stabilizer solutionscan be used, including amino trimethylene phosphonic acid; and otherorganophosphorus compounds. It should be appreciated that the reactionsbetween hydrogen peroxide and hydrocarbons are not per se of the presentinvention, and the invention encompasses use of various catalysts andother additives which facilitate or accelerate these reactions as areknown in the art.

The invention is further illustrated in the following example, which isillustrative of the efficacy of the present invention, without being,however, intended to be delimitative thereof.

EXAMPLE

In this Example the site remediated pursuant to the invention was anabandoned lamp manufacturing plant at which a subterranean groundwaterreservoir similar to that in FIGS. 1 and 2 was present, which washeavily contaminated with hydrocarbons and chloroethanes. Four wellswere sunk into the reservoir, generally about the periphery of thereservoir. Initial BTEX and chloroethane contamination was measured, andare shown in Table I.

In order to establish the acceptability of continuity and well interflowpaths, an 80% acetic acid solution was injected into Well No. 1(situated updip in the groundwater reservoir structure) at a rate of 6gallons per minute for a period appropriate to provide 0.1% by weight ofthe effective volume of contaminated water in the reservoir. Theeffective volume included the relatively porous overburden and a 10%additive factor based on groundwater reservoir structure extendingbeyond the cleanup site boundaries. pH at Wells No. 2, 3 and 4 at thestart of the test flow was 6.9 avg. After a period of 1 day, pH wasfound to have dropped to 5.5 at No. 2, to 6.1 at No. 3, and to 6.7 atNo. 4, indicating acceptable continuity and well interflow paths.

In a first cycle of treatment 1.4% by weight of the effectivecontaminated water volume to be treated, of the 80% acetic acidsolution, followed by 20% ferrous sulfate solution, followed by a 35% H₂O₂ solution was injected via each well at a rate of 6.0 gallons perminute with injection quantities of 120, 240, 90, and 120 gallonsrespectively. After 7 days, measurements of the BTEX and chloroethanelevels at the four wells were determined.

One month later the same injection procedure was repeated using the same1.4% of treating solution (by weight of the effective volume ofcontaminated groundwater). BTEX measurements were repeated 10 days afterthe second injection. Data for the foregoing are tabulated in Table Ibelow:

                  TABLE I                                                         ______________________________________                                                  Well 1                                                                              Well 2    Well 3  Well 4                                      ______________________________________                                        Initial     1.8     1100      30    0.7                                       Total BTEX  10.2    1.6       1.9   1.1                                       Chloroethane                                                                  (ppm)                                                                         First       1.4     1.4       1.4   1.4                                       Treatment                                                                     (%)                                                                           Total BTEX  0.01    0.05      0.01  0.01                                      Chloroethane                                                                              5.3     0.40      0.36  0.11                                      (ppm)                                                                         Second      1.4     1.4       1.4   1.4                                       Treatment                                                                     (%)                                                                           Total BTEX  0.08    ND*       0.03  ND*                                       Chloroethane                                                                              0.09    0.16      0.006 0.007                                     (ppm)                                                                         ______________________________________                                         *Non-Detectable                                                          

The reduction in BTEX levels is seen to be remarkable. The BTEX waspartially in a free-product phase on top of the groundwater, so most ofthe free cycle chemistry was used up in reducing this free-product.

While the present invention has been particularly set forth in terms ofspecific embodiments thereof, it will be understood in view of theinstant disclosure that numerous variations on the invention are nowenabled to those skilled in the art which variations yet reside withinthe present teachings. Accordingly the invention is to be broadlyconstrued and limited only by the scope and spirit of the claims nowappended hereto.

What is claimed is:
 1. A method for remediating ahydrocarbon-contaminated region of a subterranean body of groundwater todestroy or reduce the initial concentration levels of hydrocarboncontaminants, comprising the steps of:(a) providing a plurality ofmutually spaced wells intersecting said groundwater region; (b)providing a treating flow of acetic acid from one or more of said wellsinto said groundwater region, to establish acidic conditions therein;(c) introducing a turbulent flow of an aqueous solution of ferrous ioninto said groundwater region, for mixing with said acidifiedgroundwater, thereby providing a catalyst for disassociation of hydrogenperoxide; and (d) providing a treating flow of hydrogen peroxidesolution from one or more of said wells into said groundwater region,said hydrogen peroxide undergoing a Fenton-like reaction in the presenceof said acidic conditions and said ferrous ion to generate hydroxyl freeradicals for oxidizing said contaminants.
 2. A method in accordance withclaim 1, wherein in step (a) said groundwater region is brought to a pHof from 3.0 to 4.0.
 3. A method in accordance with claim 1, whereinduring step (b) the existence of acceptable continuity and wellinterflow paths for the said region are determined by monitoring pHchanges at each other of said wells as a function of time to detect a pHdrop of at least 0.2.
 4. A method in accordance with claim 1, whereinbetween steps (b) and (c) and between steps (c) and (d) potable water isinjected from the same said wells in place of acetic acid and ferrousion solutions, to provide a transient buffer zone between thecompositions introduced during steps (b), (c) and (d), thereby delayingthe reaction of step (d) until the plume of injected miscible reactantshas extended further into said groundwater region.
 5. A method inaccordance with claim 1, wherein said acetic acid is flowed as asolution at a rate of 5 to 10 gallons/min.
 6. A method in accordancewith claim 5, wherein said solution includes from 10% to 100% by weightof acetic acid.
 7. A method in accordance with claim 1, wherein thetotal amount of acetic acid flowed into said region is from 1 to 3% byvolume of the effective volume of contaminated water which is treated,based on a 100% acetic acid solution.
 8. A method in accordance withclaim 7, wherein the Fe²⁺ ion is provided as an aqueous solution offerrous sulfate heptahydrate, the total volume of said solution flowedinto said region being from 0.5 to 3% of the effective volume of thecontaminated water which is treated, based on a 100% by weight solutionof said heptahydrate.
 9. A method in accordance with claim 8, whereinthe treating flow of said hydrogen peroxide is at the rate of 0.1 to 10gallons of hydrogen peroxide per minute per well, expressed on the basisof a 35% by weight solution of hydrogen peroxide.
 10. A method inaccordance with claim 1, wherein the total said treating flow ofhydrogen peroxide solution is 1 to 5% by weight of the effective volumeof contaminated water which is treated, expressed on the basis of a 100%solution of hydrogen peroxide.
 11. A method is accordance with claim 1,wherein the treating flows of steps (a), (b) and (c) are provided undera pressure not more than the hydrostatic head relative to surface at thepoint of treating flow discharge from said well.
 12. A method inaccordance with claim 11, wherein the treating flow is provided under apressure of from 6 to 40 psig.
 13. A method in accordance with claim 11,wherein the total said treating flow of hydrogen peroxide solution is0.1 to 10% by weight of the effective volume of contaminated water whichis treated, expressed on the basis of a 35% solution of hydrogenperoxide.
 14. A method in accordance with claim 1, further includingdetermining the existence of acceptable continuity and well interflowpaths for the said region by generating a test flow of a solution ofhydrogen peroxide or acetic acid from one of said wells and monitoringpH changes at each other of said wells as a function of time to detect apH drop of at least 0.2.
 15. A method in accordance with claim 14,wherein the total volume in the test flow is 0.05 to 0.1% by weight ofthe effective volume of contaminated water, expressed on the basis of a35% solution of hydrogen peroxide, and is injected at the rate of 0.3 to10 gallons/minute and at a pressure which is not more than thehydrostatic head relative to surface at the point of treating flowdischarge from said well.
 16. A method in accordance with claim 1,including at least 3 said wells, which are spaced about the periphery ofsaid groundwater region.
 17. A method in accordance with claim 14,wherein said test flow is injected at one said well and the said pHchange monitored at said other wells.
 18. A method in accordance withclaim 14, further including in step (b), monitoring temperature changesat one or more other of said wells to detect a temperature rise of atleast 2° F. as a confirmatory indicator of said acceptable continuityand well interflow paths.
 19. A method in accordance with claim 1,wherein at least one of said treating solutions further includes areaction surface enhancing reagent.
 20. A method in accordance withclaim 1, wherein the treating flow is periodically stopped and thehydrocarbon contaminant levels measured at each said well, until thesaid initial contaminant concentration levels drop below predeterminedacceptable values.
 21. A method of remediating ahydrocarbon-contaminated subterranean static plume of groundwater todestroy or reduce the initial concentration levels of hydrocarboncontaminants, comprising the steps of:(a) providing a plurality ofmutually spaced wells intersecting said static plume groundwater; (b)measuring the change in water depth at each of said wells followingatmospheric precipitation, to determine by common depth changes thelikelihood of said plume; (c) confirming the existence of the staticplume by generating a test flow of a solution of hydrogen peroxide oracetic acid from one of said wells and monitoring the absence of pHchanges at each other of said wells as a function of time; and (d)providing a treating flow of solutions of acetic acid, of ferrous ion,and of hydrogen peroxide from each of said wells to establish a radialsweep about each said well, the total volumes and respectiveconcentrations of treating solutions being effective to bring about aFenton-like reaction generating hydroxyl free radicals for oxidizingsaid contaminants.
 22. A method for remediating ahydrocarbon-contaminated region of a subterranean body of groundwater todestroy or reduce the initial concentration levels of hydrocarboncontaminants, comprising:establishing acidic conditions at saidgroundwater region; and introducing flows of aqueous solutions offerrous ion and of hydrogen peroxide into said groundwater region, formixing with said acidified groundwater; said hydrogen peroxideundergoing a Fenton-like reaction in the presence of said acidicconditions and said ferrous ion to generate hydroxyl free radicals foroxidizing said contaminants.
 23. A method in accordance with claim 22,wherein said groundwater region is acidified to a pH of from 3.0 to 4.0.24. A method in accordance with claim 23, wherein said acidic conditionsare brought about by introducing a flow of an acetic acid solution; thetotal amount of acetic acid flowed into said region being from 1 to 3%by volume of the effective volume of contaminated water which istreated, based on a 100% acetic acid solution.
 25. A method inaccordance with claim 24, wherein the Fe²⁺ ion is provided as an aqueoussolution of ferrous sulfate heptahydrate, the total volume of saidsolution flowed into said region being from 0.5 to 3% of the effectivevolume of the contaminated water which is treated, based on a 100% byweight solution of said heptahydrate.
 26. A method in accordance withclaim 25, wherein the total amount of treating solution of hydrogenperoxide solution is 1 to 5% by weight of the effective volume ofcontaminated water which is treated, expressed on the basis of a 100%solution of hydrogen peroxide.